This invention relates to magnetic disk drives and, more particularly, to a switch for interchanging the electronic systems in a two spindle disk drive.
High capacity magnetic disk drives include a plurality of magnetic disks rotated on a common spindle. Fixed disk drives such as the IBM 3350 and Storage Technology Corporation 8350/8650/8370 disk drives include two spindles in each drive. The spindles, disks, magnetic heads, actuator, and associated circuitry are referred to as a "head/disk assembly" (HDA). Each head/disk assembly has its own electronic system which has logic circuitry for processing the digital data signals written onto and read back from the magnetic disks. The electronic systems also include circuitry for generating spindle and head addresses, which control the actuators to access particular tracks on the disks. The electronic systems communicate with a bus connected to the disk controller and the host computer.
In many applications, it is very important to have continuous access to the data on the disks. For example, some time sharing customers require continuous data availability even when one of the electronic systems fail. In accordance with current practice, when one of the electronic systems fails, a field engineer is called and he can switch the head/disk assembly to an alternate electronic system.
Movable media disk drives provide more flexibility because the disk cartridge or pack can be removed or placed on another machine. However, this alternative is not available in high capacity fixed media drives of the type under consideration.
It is an object of the present invention to significantly reduce the period of data inaccessibility during unscheduled interruptions of magnetic disk drive operation.